Electrical power in cars
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  1. #1
    Member RASTEVE's Avatar
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    Default Electrical power in cars

    Hey, does anyone know whether using say a 400 watt appliance through a 12 volt inverter increases fuel consumption?

    On a similar topic, how many amps or how much power does an alternator (diesel preferably) deliver?

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  2. #2
    Contented Peugeot Driver addo's Avatar
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    It certainly increases fuel consumption to run a current draw on your car. The alternator increases its physical resistance to turning in response to raised field current - which is brought about by increased demand on the system. You work the alternator hard; it then taxes the motor.

    Dunno about diesels but alternators in petrol powered cars now are pretty high output because they're well-challenged. (Blower fans for electronic ignitions, A/C, loud stereos, driving lights, other accessories...) 65A would probably be considered small.

    I've looked at some of the uS made high output alternators and wondered, then I note how often people on American car forums are kvetching about their alternator dying again! We pay too much here, for me to be willing to take a punt on the unknown.

    Cheers, Adam.

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    Fellow Frogger! jarrods's Avatar
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    The formula for power is P(Watts)=Volts X Amps

    Your fuel consumption will increase marginally. You are however putting a heavy load on your alternator. Using the above formula You are drawing 33 amps from your alternator plus inverter losses to run the 400W appliance. This could be up to 40 amps depending on your inverter. If you have a 55 amp alternator this doesn't leave much for running the car and charging the battery particularly if it's dark. Your alternator should have a stamp on it somewhere saying what size it is.
    Also make sure you have decent size cable from the battery to the inverter. The cigarette lighter socket will be unsuitable for this. What is the appliance, is it drawing 400W constantly?

    Jarrod

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    Member RASTEVE's Avatar
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    Quote Originally Posted by jarrods
    The cigarette lighter socket will be unsuitable for this. What is the appliance, is it drawing 400W constantly?
    Anyway, speaking of losers, I had an idea that I could use a modified 1970's birko under the bonnet of my car to heat vegie oil to make it runny enough to put though my pug. It's a 400 watt birko with about a litre capacity. I was thinking that it'd be great to do the initial heating using house mains power, and then use a thermostat device to just keep the temperature of the oil about 80 degrees under alternator power, so it should just be "on" power for a few seconds every now and then to keep the oil hot.

    Thanks for your responses.
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  5. #5
    WLB
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    Quote Originally Posted by RASTEVE
    Anyway, speaking of losers, I had an idea that I could use a modified 1970's birko under the bonnet of my car to heat vegie oil to make it runny enough to put though my pug. It's a 400 watt birko with about a litre capacity. I was thinking that it'd be great to do the initial heating using house mains power, and then use a thermostat device to just keep the temperature of the oil about 80 degrees under alternator power, so it should just be "on" power for a few seconds every now and then to keep the oil hot.

    Thanks for your responses.
    It would probably be much easier to use the usual veg oil method using hot water from the car's cooling system to heat the fuel tank and lines and liquefy the oil if it solidifies. This heat is free; or rather, you've already paid for it and it just gets thrown away. When the engine is cold and the oil too thick, you start and run on diesel fuel until the cooling system warms up.

    Beware of using electric elements to heat the oil unless you've got adequate safeguards to limit temperature if anything goes wrong with the thermostat as you might take the oil to flashpoint and have a fire on your hands.

    Warwick.

  6. #6
    1000+ Posts alan moore's Avatar
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    A 30 Amp discharge to run your heater is fairly huge. In my experience an alternator rated at say 100A would last about 3 mins at this before it blew up. A 100A alternator may push 50A for extended periods but even that is pushing it. Use the hot coolant idea.

    You only have to look at the size of the conductor away from these 100A units to realise that these output figures are optimistic.
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    Fellow Frogger! Decca's Avatar
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    could you extend the glow plug feed and have a plug, or two, heating up the oil in a small container like a modified fuel filter??


    Decca
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    WLB
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    Quote Originally Posted by Decca
    could you extend the glow plug feed and have a plug, or two, heating up the oil in a small container like a modified fuel filter??


    Decca
    Glow plugs draw a lot of power and glow red hot. Not good to immerse in a combustible liquid.

  9. #9
    1000+ Posts CHRI'S16's Avatar
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    Or just buy a 12V heater and run an auxilary battery.... set up everything else as described... - Chris
    ... ptui!

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    Quote Originally Posted by WLB
    Glow plugs draw a lot of power and glow red hot. Not good to immerse in a combustible liquid.
    But there's no oxgen, so it would be OK i assume?
    its like a fuel pump, sure is sparking while fuel is going through it, but there's no air to make it ignite...

  11. #11
    1000+ Posts CHRI'S16's Avatar
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    Quote Originally Posted by nate
    But there's no oxgen, so it would be OK i assume?
    its like a fuel pump, sure is sparking while fuel is going through it, but there's no air to make it ignite...
    But a fuel pump makes no electrical or hi-temp heat conection like the glow plug. An electric fuel pump makes a pure mechanical conection with the fuel.
    In any oil there could be small air bubbles in the oil, or it will boil it, exposing water to steam which could start a fire...lets give a try anyway man!. .. - Chris
    ... ptui!

  12. #12
    WLB
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    Quote Originally Posted by nate
    But there's no oxgen, so it would be OK i assume?
    its like a fuel pump, sure is sparking while fuel is going through it, but there's no air to make it ignite...
    If you heat it to flashpoint or boil it in a closed container it won't be long before there is air present. Something will give and the hot oil will be released.
    Fuel pumps have been designed with all the possibilities taken into account.

    Warwick.

  13. #13
    WLB
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    The typical flashpoint of cooking oil will be around 300 to 350 degrees C. A glow plug runs at around 1,000 degrees. It glows. Not a good combination unless it has been properly designed as a system with lots of safeguards and fail-safe controls.

    Warwick.

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